1. Field of the Invention
This invention relates generally to structural materials and more particularly to a method for making hollow unitary structures which may be of homogeneous composition. A novel fluid cooled unitary mirror structure for reflecting high intensity coherent electromagnetic radiation is disclosed as one product of the method of this invention.
2. State of the Prior Art
Various methods have been used in the past for the manufacture of hollow structures, resulting in the production of a wide variety of hollow, relatively lightweight structures.
Prior art relevant to the particular mirror structure described herein includes the sandwich panel structures made by laminating a low density cellular or honeycomb core structure between a pair of outer surface sheets or skins. Such panels are largely hollow and therefore lightweight, but possess a high stiffness-weight ratio. In the past, both the cellular core and the outer face sheets were prefabricated and then bonded to make the structural panel. Typically the bonding was achieved by either use of adhesive or by the welding or brazing together of the component parts.
Thus U.S. Pat. No. 2,814,717 to Hardesty issued Nov. 26, 1957, teaches a method of resistance welding for securing thin sheet metal to a supporting core structure.
U.S. Pat. No. 2,609,068 to Pajak issued Sept. 2, 1952, and U.S. Pat. No. 2,952,579 to Merriman issued Sept. 13, 1960, both disclose methods of adhesively bonding a metal foil honeycomb core between a pair of outer sheets.
U.S. Pat. No. 2,962,403 to Jones issued Nov. 29, 1970 discloses a structural panel made by laminating, by means of adhesive, an intermediate honeycomb core and a pair of outer wire screen facings.
Applicant is further aware of the following patents relevant to methods of electro-deposition of material on a mesh or other apertured structure:
U.S. Pat. No. 2,529,237 to Turner issued Nov. 7, 1950 teaches open work electrodes, including wire mesh, for the electro recovery of metals. The open work electrode is embedded in a deposit of metal resulting in a solid slab of material. The use of thin mesh of a suitable material made it unnecessary to separate the much larger mass of recovered metal from the electrode, which separation had been a source of difficulties until then. Also, the mesh could be made of the same metal and degree of purity as the recovered metal thus being essentially indistinguishable therefrom.
U.S. Pat. No. 3,686,089 to Butter et al. discloses a method for embedding structural reinforcing material in a matrix produced by electroplating means.
U.S. Pat. No. 1,323,167 to Denny issued Nov. 25, 1919 teaches the production of reinforced metal elements formed by electroplating a relatively soft metal onto a perforated foundation of more rigid metal. The covering metal fills the perforations and is thereby mechanically locked to the foundation.
The use of adhesives to achieve a hollow lightweight structure as described in the referenced patents does not produce a highly reliable joint between the core and the outer face sheets, particularly under difficult environmental conditions. In some situations, it may be desirable to immerse the structure in a fluid or expose it to extreme temperatures, either of which would tend to weaken the adhesive bond.
Welding methods of assembly are difficult, particularly where complex structures are attempted or where any portion of the structure includes thin metallic foils such as are often used in lightweight honeycomb structures. Welded joints often have hidden defects which are not readily apparent until a structural failure occurs.
It is, therefore, one object of this invention to provide a method of making hollow structures of unitary construction without use of adhesive bonding or welding.
It is another object of this invention to provide a method of making hollow structures including complex internal manifolds and cavities requiring less difficult and costly machining techniques.
It is yet another object of this invention to provide a method of making complex hollow structures of unitary construction and homogeneous composition.
It is a further object of this invention to provide a method of making lightweight structures of superior structural and dimensional stability and reliability under a wide range of adverse environmental conditions.
It is another object of this invention to provide a method of making hollow structures of unitary construction having internal structural elements and external wall surfaces, which method allows wide latitude of control over a continuous range of the thickness of the internal structural elements relative to the exterior walls of the hollow structures.
It is an additional object of this invention to provide a method of making fluid cooled structures of unitary construction and homogeneous composition having internal manifolds for circulating fluids.
It is also an object of this invention to disclose a method of making hollow, arbitrarily complex structures of unitary construction and homogeneous composition of a wide variety of materials.
It is a further object of this invention to provide a fluid cooled mirror structure of unitary construction and homogeneous composition for use at high temperatures.
It is another object of this invention to provide a fluid cooled mirror structure of unitary construction having superior thermal transfer characteristics and low thermal mass.
It is yet another object of this invention to provide a fluid cooled mirror structure having superior optical and dimensional stability over a wide temperature range.